Research has shown that compared to high frequency alarm tones (on the order of 3 kHz), low frequency alarm tones on the order of a 520 Hz, fundamental frequency, square wave can be more effective in awakening children from sleep and can be better heard by people with high frequency hearing deficit which often accompanies advanced age or those exposed to loud sounds for extended periods of time. One of the problems in utilizing a such a low frequency (pitch) alarm tone is that it takes more electrical driving power for an audio output transducer to emit a low frequency alarm tone (for example ˜520 Hz) than to emit a higher frequency alarm tone (for example 3 kHz) at comparable sound pressure levels interpreted as loudness by humans. This problem is compounded when a low frequency alarm tone is desired to be used in a life safety device such as a conventional environmental condition detector such as a smoke detector or carbon monoxide detector or a combination smoke and carbon monoxide detector, as non-limiting examples, since such detector unit components including the sound producing elements are typically contained within a housing a few inches tall (˜2-3 inches thick in outside dimension) and approximately three to six inches in diameter or approximately square planform. Due to these geometric constraints (largely for a non-intrusive décor and aesthetics), it is difficult to use a normal, quarter wave, resonant cavity comprising a tube with one open end and one closed end (Helmholtz resonant cavity or resonator). Based on the theory of acoustics, the length of such a resonating cavity (resonator) should be on the order of one quarter of a wavelength of the fundamental frequency to obtain resonance which reinforces (amplifies) the sound output of an audio output transducer (for example a speaker or piezoelectric transducer) acoustically coupled to a resonant cavity. For example, for a fundamental frequency of 520 Hz, a quarter-wave, closed end, resonant cavity with an open opposite end would theoretically need to be approximately 6.5 inches long for air at standard sea level conditions where the speed of sound is approximately 1120 ft/sec. Practically however, allowing for end effects of the open end of the cavity, the length of such a quarter-wave, resonant cavity is on the order of 5 inches, still about twice the dimension of the thickness of the housing of a conventional environmental condition detector. Further, in order to get the requisite sound pressure level with conventional battery power used in environmental condition detectors (single 9V alkaline battery or 2-4 AA alkaline batteries for example), the audio output transducer needs to be on the order of at least 1.75 inches in diameter in one embodiment of the invention. Given this diameter along with a length on the order of 5 inches from the example above, it is easily determined that this size resonant cavity would occupy so much volume inside the housing of a life safety device configured as a conventional environmental condition detector that it would likely cause major issues with the omni-directional inlet airflow qualities required in smoke and carbon monoxide detectors for maximum sensitivity and/or also result in much larger housing dimensions than are conventional for such life safety devices. Therefore, while a resonant cavity is a very useful element to amplify the sound pressure output of an audio output transducer coupled to the resonant cavity forming an audio output apparatus, it is clear that a conventional, non-folded, quarter wave, resonant cavity is not as geometrically suitable for conventionally shaped and sized environmental condition detectors as a more compact quarter wave, resonant cavity would be for this application. It is noted that the current trend, in particular for smoke detectors and carbon monoxide detectors designs, is to have a smaller overall spatial profile to be less intrusive into the décor of residences and commercial installations.